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Abstract:

The invention is directed to a drive belt such as a transport or
synchronous or power transmission belt with an elastomeric belt body
having a drive side and a back side, a tensile member embedded in the
belt body, and an anti-static, wear-resistant, covering fabric on at
least one of the drive and back side. The anti-static fabric includes a
nonconductive natural or synthetic polymeric fiber and a conductive
fiber. The conductive fiber is a synthetic polymeric fiber with a
conductive metallic coating. The metallic coating may be silver.

Claims:

1. A drive belt comprising an elastomeric belt body having a drive side
and a back side, a tensile member embedded in said body, and a covering
fabric on at least one of said drive and back side; said fabric
comprising a polymeric fiber and a conductive fiber.

9. The belt of claim 8 wherein said conductive filler is one or more
selected from the group consisting of carbon black, graphite, carbon
fiber, metallic powder, metallic fiber, and carbon nano-tubes.

10. The belt of claim 1 wherein the fabric comprises from about 10% to
about 40% by weight of the conductive fiber.

11. A drive belt comprising an elastomeric belt body having a drive side
and a back side, a tensile member embedded in said body, and a covering
fabric on at least one of said drive side and back side; said fabric
comprising a first polymeric fiber and a conductive fiber; said
conductive fiber comprising a second polymeric fiber with a metallic
silver coating.

12. The belt of claim 11 wherein said fabric comprises warp yarns and weft
yarns, said conductive fiber present in at least one warp yarn and at
least one weft yarn.

13. The belt of claim 12 wherein said second polymeric fiber comprises
polyamide or polyester.

14. The belt of claim 13 wherein said first polymeric fiber comprises
polyamide or polyester.

15. A belt drive system comprising a belt and at least one drive component
comprising a thermoplastic resin friction partner; said belt comprising
an elastomeric belt body having a drive side and a back side, a tensile
member embedded in said body, and a covering fabric on at least one of
said drive and back side; said fabric comprising a polymeric fiber and a
conductive fiber.

16. The belt drive system of claim 15 wherein said resin is one or a blend
of more than one selected from the group consisting of
ultra-high-molecular-weight polyethylene, polyamide, polyphenylene
sulfide, acetal, and polyetheretherketone.

17. The belt drive system of claim 15 wherein said resin is
ultra-high-molecular-weight polyethylene or polyamide.

18. The belt drive system of claim 15 wherein the drive component is a
sprocket, pulley, tensioner, slider or idler.

19. The belt drive system of claim 15 wherein said resin comprises a
conductive filler.

20. The belt drive system of claim 15 wherein the conductive fiber is a
polymeric fiber with metallic coating.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]This invention relates generally to thermoplastic belting, more
particularly to belting with wear-resistant, anti-static fabric on a
surface, and specifically to a drive belt with fabric cover containing
silver-coated polymeric fiber.

[0003]2. Description of the Prior Art

[0004]Thermoplastic polyurethane ("TPU") drive belts are used for
transport applications, as well as for power transmission, motion
control, and timing applications. TPU belts may be in the form of flat
belts, toothed belts, V-belts, multi-v ribbed belts or other special
profiles. They are typically electrically insulating. It is sometimes
desirable that the belts not retain electrostatic charges, i.e., that the
belts have anti-static properties.

[0005]Anti-static properties generally include one or more of the
following characteristics: surface resistance lower than 108 ohms;
volume resistance lower than 109 ohms; and ground bleeder resistance
lower than 106 ohms/meter. Standards such as BS PD CLC/TR
50404:2003, DIN EN 13463-1, and IEC 60079-0 provide information on the
avoidance of hazards due to static electricity.

[0006]U.S. Pat. No. 4,767,389 discloses a flat, plastic-covered-textile
belt with anti-static properties arising from either an electrically
conductive filament in the threads of the textile supporting element or
an electrically conductive layer between the textile support and plastic
covering. The conductive filament may be metal or carbon fiber, and the
conductive layer may be soot-containing plastic. The plastic covering may
be thermoplastic polyurethane. U.S. Pat. No. 7,328,785 teaches a
conductive timing belt having a conductive layer of thermoplastic on the
tooth surface. The thermoplastic may be conductive from the use of
conductive microfibers, graphite or carbon black mixed therein.

[0007]U.S. Pat. No. 6,228,448 teaches use of an electrically conductive
elastomeric surface ply which is preferably doped with a sufficient
amount of carbon black or other conductive additives to give the outer
ply or entire endless belt a surface resistivity of less than about 1014
ohm/square.

[0008]Metal chains are sometimes used in transport or conveying
applications requiring conductivity or anti-static behavior, but the
associated lubrication problems and noise are undesirable in many
situations.

[0009]U.S. Pat. No. 5,417,619 teaches a covering canvas impregnated with
an anti-static rubber composition based on conductive carbon black. An
unwanted side effect of such coatings is a decrease in the abrasion
resistance of the fabric resulting in rapid loss of the anti-static
effect during use. The resulting abraded particles can be detrimental to
nearby electronic or electrical components or systems. U.S. Pat. No.
5,351,530 makes use of such loss of conductivity to indicate the state of
wear of a conductive-rubber-coated fabric.

[0010]It is known to incorporate so-called conductive carbon black or
graphite in rubber and plastics to provide anti-static properties to the
rubber or plastic composition. These compositions also generate
undesirable abrasion products.

[0012]The invention is directed to a drive belt such as a transport or
synchronous or power transmission belt with an elastomeric belt body
having a drive side and a back side, a tensile member embedded in the
belt body, and a covering fabric on at least one of the drive and back
side. The fabric includes a nonconductive natural or synthetic polymeric
fiber and a conductive fiber. In a preferred embodiment, the conductive
fiber is a synthetic polymeric fiber with a conductive metallic coating.
The conductive metallic coating is preferably silver. The fabric may have
warp threads and weft threads, and the conductive fiber may be present in
either or both of the warp and weft threads. In a preferred embodiment,
the non-conductive fiber is a mixture of polyester and nylon fibers and
the conductive fiber is continuous polyester fiber coated with silver.

[0013]The invention is also directed to a belt drive system having a drive
belt as described above and at least one friction partner, such as a
sprocket, pulley, slider or idler, made of a metal or a thermoplastic
molding resin. Nonlimiting examples for the molding resin include nylon
or polyamide ("PA"), polyphenylene sulfide, acetal,
ultra-high-molecular-weight polyethylene ("UHMWPE"),
polyetheretherketone, or the like, and the resin may be compounded with
fillers, friction modifiers, fibers, stabilizers and/or the like. When
the inventive belt is used with an UHMWPE friction partner, the friction
coefficient is 2.5 to 6 times lower than observed with conventional nylon
fabrics and UHMWPE. The inventive belt also has improved abrasion
resistance over conventional belts, and the anti-static properties remain
even after long term use.

[0014]The foregoing has outlined rather broadly the features and technical
advantages of the present invention in order that the detailed
description of the invention that follows may be better understood.
Additional features and advantages of the invention will be described
hereinafter which form the subject of the claims of the invention. It
should be appreciated by those skilled in the art that the conception and
specific embodiment disclosed may be readily utilized as a basis for
modifying or designing other structures for carrying out the same
purposes of the present invention. It should also be realized by those
skilled in the art that such equivalent constructions do not depart from
the spirit and scope of the invention as set forth in the appended
claims. The novel features which are believed to be characteristic of the
invention, both as to its organization and method of operation, together
with further objects and advantages will be better understood from the
following description when considered in connection with the accompanying
figures. It is to be expressly understood, however, that each of the
figures is provided for the purpose of illustration and description only
and is not intended as a definition of the limits of the present
invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]The accompanying drawings, which are incorporated in and form part
of the specification in which like numerals designate like parts,
illustrate embodiments of the present invention and together with the
description, serve to explain the principles of the invention. In the
drawings:

[0016]FIG. 1 is a partially fragmented perspective view of a drive belt
according to an embodiment of the invention;

[0017]FIG. 2 is a schematic representation of a test used to characterize
an aspect of the present invention;

[0018]FIG. 3 is a schematic representation of another test used to
characterize an aspect of the present invention; and

[0019]FIG. 4 is a schematic representation of another test used to
characterize an aspect of the present invention.

DETAILED DESCRIPTION

[0020]FIG. 1 illustrates the construction of a toothed drive belt
according to an embodiment of the invention. In FIG. 1, belt 40 is formed
of an elastomeric body 42 in which is embedded a strain-resistant tensile
cord 20. A series of cogs or teeth 44 are disposed on the underside of
the belt and adapted to mesh with corresponding teeth of a sprocket in
gear-like fashion to transmit power or motion without slipping. Belt 40
employs a textile fabric 15 at the back side 13 or back surface of the
belt. A layer 17 of elastomer may be interposed between cord 20 and the
back fabric 15. During processing the elastomer material of layer 17 may
penetrate the back fabric 15. The layer 17 and body 42 may be of the same
elastomeric material, for example a thermoplastic polyurethane ("TPU") or
a rubber compound or the like. The layer 17 the body 42 or both may be
compounded with an antistatic ingredient or conductive filler such as
carbon black, conductive carbon black, graphite, carbon fiber, metallic
powder, metallic fiber, carbon nano-tubes, or the like, present in an
amount sufficient to impart a desired level of conductivity to the body
elastomer. Belt teeth 44 also carry a textile fabric 46 on the drive side
of the belt. Either the back fabric 15, the tooth fabric 46, or both may
be anti-static, wear-resistant fabric according to embodiments of the
invention. Other types of belts may be used in embodiments of the
invention, including flat belts, V-belts, dual profile belts, belts with
different profiles or purposes, and the like.

[0021]The anti-static, wear-resistant fabric is conductive because it
contains conductive fibers having a metallic component such as a metallic
coating. Preferably the metallic component of the conductive fibers is
silver. A preferred conductive fiber is a polymeric fiber which may be
synthetic or natural and which is coated with metal. The metallic coating
may be silver, gold, platinum, copper, nickel, tin, zinc, palladium, or
an alloy thereof. Preferably silver is the metallic coating on the
conductive fiber. One or more of the conductive fibers may be blended
with non-conductive natural or synthetic polymeric fibers to form a
conductive yarn. The conductive yarn may be used in either the warp or
the weft or both directions of a woven conductive fabric. The conductive
fiber is preferably continuous fiber. Nonlimiting examples of conductive
fibers believed to be useful in embodiments of the invention include
those disclosed in U.S. Pat. Nos. 4,427,596, 5,000,980, 6,703,123, and
6,710,242, which are hereby incorporated herein by reference.

[0022]The anti-static, wear-resistant fabric may be woven of weft and warp
yarns or threads, knitted, or non-woven. Any suitable weave or knit may
be used, such as square weave, twill weave, or the like. A 2×2
twill may be used. The non-conductive polymeric fibers, as well as the
base fibers of the metal-coated conductive fibers, may be any desired
natural or synthetic fiber, such as polyester, nylon or polyamide ("PA"),
acrylic, cotton, rayon, aramid, or the like. The fibers may be textured,
twisted, blended, or the like. Hybrid, composite, or blended threads may
be random fiber mixtures, twisted or cabled yarns or threads of various
types, or structured such as wrapped or core-sheath yarns. Preferred
fibers are polyester and polyamide, including PA-66.

[0023]According to an embodiment of the invention, a drive belt may have
an elastomeric belt body having a drive side and a back side, a tensile
member embedded in said body, and a covering fabric on either the drive
side, or the back side or both sides. The fabric may have a first
polymeric fiber and a conductive fiber, and the conductive fiber may be
of a second polymeric fiber with a metallic silver coating. The first and
second polymeric fibers may be of the same polymer, such as polyester or
polyamide, or they may be of different polymers. The conductive fiber may
be in the warp threads of the fabric, or in the weft threads of the
fabric, or in both. The conductive fiber may be present or exposed at the
fabric surface or surfaces.

[0024]In an embodiment of the invention, the conductive fiber may make up
from about 10% to about 40% of the total weight of the fabric. In another
embodiment, the fabric may be about 10% to 40%, or from 20% to 30%
conductive fiber and the remainder of the fibers a combination of
polyester fibers and polyamide fibers.

[0025]The fabric may be treated or coated with one or more primer,
adhesion promoter, adhesive, friction modifier or binder. The fabric may
be laminated to a thermoplastic film for example to prevent penetration
of the elastomer of the belt body during manufacture. Other fabric
variations may used as desired.

[0026]The tensile cord, if present, may be any known in the art. For
example, the cord may include fibers of aramid, nylon, polyester, rayon,
glass, metal, carbon, or the like, or combinations thereof.

[0027]When the conductive fiber is silver-coated polyester or polyamide,
it has been found that certain frictional and wear characteristics of the
inventive belt can be significantly improved. The following examples
illustrate this effect. In each example the anti-static fabric comprised
about 57% polyester fiber, about 20% polyamide fiber, and about 23%
conductive fiber, with the conductive fiber present in both warp and weft
yarns. The conductive fiber was silver-coated polyester fiber. The fabric
was woven and the weight was about 200 g/m2. In each comparative
example, a conventional PA-66 woven fabric was used.

[0028]In a first test series, Belt Example 2 ("Ex." 2) was constructed
with polyurethane belt body and silver-containing anti-static fabric on
the tooth surface. The toothed belt of Ex. 2 was endless with a metric
T10 profile (10 mm pitch, and trapezoidal tooth shape) and with a length
of 1250 mm, i.e. 125 teeth. Comparative Example 1 ("Comp. Ex. 1") was
constructed the same as Ex. 2 but with a conventional PA-66 woven fabric
on the tooth surface.

[0029]Specimens of these two belts were subjected to a friction test, as
illustrated schematically in FIG. 2. In FIG. 2, belt 50 is inverted
(tooth-side out) and trained about pulleys 50 and 52. Upper span of belt
50 is slidably supported on auxiliary belt drive 54 which includes
sufficient support rollers to support the vertical force of mass 56
pressing down on the upper span of belt 50. Between mass 56 and belt 10
is fixed friction partner 58. When belt 10 is driven by pulleys 50 and 52
turning counter-clockwise, with mass 56 horizontally fixed, friction is
generated between the tips of the belt teeth and the surface of the
friction partner. The frictional temperature at the friction interface is
measured by thermometer 60, and the frictional force is measured by load
cell 62. Two different friction partners were tested, steel and UHMWPE.
The total projected area of belt under the friction partner was 3750
mm2. This total area was used to calculate the loading pressure,
even though the tooth area in actual contact with the friction partner
would be smaller.

[0030]In the testing, two load conditions were used. The standard test
conditions were room temperature (25° C.), a belt sliding speed of
0.5 m/s, and a loading pressure of 0.012 N/mm2. A high-load test
condition included the same sliding speed, but twice the loading
pressure, 0.024 N/mm2. In some tests, the sliding speed was
increased at various times to 0.75, 1.0, 1.25, or 2 m/s. Two basic types
of friction partners were tested with the inventive belt and comparative
belt described above: steel and UHMWPE. Two identical machined steel
plate friction partners were tested, but one natural and one contaminated
or coated with a thin film of PU polymer. The test results are summarized
in Table 1.

[0031]Comp. Ex. 1 belt, illustrates typical performance of conventional
belts, namely reasonably good frictional properties, but lots of abrasive
wear on the tooth fabric. After 30 days of testing, the nylon fabric is
mostly gone from the teeth. In test B, nylon against UHMWPE, the
coefficient of friction and the temperature rise is much higher than for
test A on steel.

[0032]The embodiment of the invention, the belt Ex. 2, performs better
than the comparative example with respect to abrasive wear on both steel
and UHMWPE and in frictional behavior on UHMWPE. Test C and D, for the
Ex. 2 on steel, show that on steel, the friction coefficient is fairly
high, but the abrasion resistance is very good, since no significant
damage to the belt tooth is observed. The temperature rise is pretty
high, but no thermal damage or melting was observed. Test E and F, for
Ex. 2 on UHMWPE, shows a very significant reduction in coefficient of
friction for the inventive belt at the standard load conditions.
Therefore, the test load was doubled after about 17 days, and after about
25 days, the sliding speed was increased several times over the remaining
days of the test. Surprisingly, the anti-static fabric of Ex. 2 still
showed no damage after 31 or 32 days of testing against UHMWPE. At the
highest speeds tested, and at the high-load condition, the UHMWPE
friction partner failed due to melting. Thus, Table 1 shows that an
embodiment of the invention exhibits much better abrasion resistance
against both steel and UHMWPE friction partners than a conventional
nylon-covered belt. Also, the inventive belt exhibits much better
frictional behavior with a UHMWPE friction partner than conventional
nylon-covered belts, i.e., the friction coefficient is 2.5 to 6 times
lower.

[0033]For a second belt test, based on the test illustrated in FIG. 3,
similar belt constructions were made as described above, but with a T5
pitch (5-mm) and with fabric on both the tooth or drive side and the back
side. In the test setup of FIG. 3, two matching belts 70, with T5
profile, 25 mm wide, 3140 mm length, are trained about pulleys 76 and 78
with belt teeth 72 on the inside to mesh with matching grooves in the
pulleys. The upper span of each belt 70 is slidably supported on slider
plate 80 of PA-66. Weights 84 straddle both belts with PA-66 plates 82
attached to the weights and pressing on the belts' back sides. Belts 70
move in the direction shown by the large arrow, driven by an electric
motor (not shown) turning driver pulley 76, and stop 86 forces the
weights 84 to remain stationary as the belts slide by underneath. The
belt speed is 18 m/minute, the back side contact area is 4750 mm2,
and the contact pressure is 0.016 N/mm2. The test is run
continuously, but stopped at regular intervals to check the belts and
PA-66 sliders, plates or friction partners for wear. Thus, Comp. Ex. 3
has conventional polyamide woven fabric on both tooth and back side, and
Ex. 4 has anti-static wear-resistant fabric on both tooth and back side,
and both are constructed to fit the test of FIG. 3.

[0034]For a third belt test, based on the test illustrated in FIG. 4,
similar specimens of the previous belt constructions were made, but with
a modified AT5 pitch (5-mm) and also with fabric on both the tooth and
back side. In the test setup of FIG. 4, belt 90, with the AT5 profile, 30
mm wide, 2735 mm length, is trained about pulleys 96 and 98 with belt
teeth 92 on the inside to mesh with matching grooves in the pulleys. The
upper span of belt 90 is slidably supported on slider plate 100 of steel.
Blocks 104 on the back side of belt 90 with steel plates 102 attached to
the blocks and pressing on the belt back side with a force provided by
springs 108. Belt 90 moves in the direction shown by the large arrow,
driven by an electric motor (not shown) turning driver pulley 96, and
stop 106 forces the blocks 104 to remain stationary as the belt slides by
underneath. The belt speed is 25 m/minute, the back side contact area is
3540 mm2, and the contact pressure is 0.028 N/mm2. The test is
run continuously, but stopped at regular intervals to check the belt and
steel sliders, plates or friction partners for wear. Thus, Comp. Ex. 5
has conventional polyamide woven fabric on both tooth and back side, and
Ex. 6 has anti-static wear-resistant fabric on both tooth and back side,
and both are constructed to fit the test of FIG. 4.

[0035]Table 2 shows the results of the second and third sets of belt
tests. The two-belt test of FIG. 3 is designated test G and test H on
belt Comp. Ex. 3 and Ex. 4, respectively. The one-belt test of FIG. 4 is
designated test I and test J on belt Comp. Ex. 5 and Ex. 6, respectively.
On both testers, the inventive belts, which were covered with the
anti-static fabric comprising silver-coated, conductive fibers according
to an embodiment of the invention, Ex. 4 and Ex. 6, lasted much longer
than the comparative nylon-covered belts. In particular, on tests G and
H, the inventive belt exhibited less than half the abrasive weight loss
of the comparative belt, even though test H ran longer than test G. It
should be noted that test H does not represent the full useful life of
the belt on the test, because the test was stopped due to equipment
issues. Likewise, on tests I and J, the inventive belt lasted nearly
twice as long as the comparative belt, at which time the abrasive weight
loss was approximately the same for both belts, but on test I the
comparative belt exhibited lots more abraded filaments exposed on the
belt back than observed on the inventive belt.

[0036]After the tests the inventive belt embodiments of Ex. 4 and Ex. 6
were examined for conductivity or anti-static properties. The volume
resistance and surface resistance were at least lower than 10,000 Ohms at
100 Volts, indicating good static conductivity. Certified conductivity
test results were not yet completed at the time of filing.

[0037]The invention is also directed to a belt drive system having a drive
belt as described above and at least one friction partner, such as a
sprocket, pulley, slider or idler, made of a metal or preferably a
thermoplastic molding resin. Nonlimiting examples for the molding resin
include nylon or polyamide, polyphenylene sulfide, acetal,
ultra-high-molecular-weight polyethylene, polyetheretherketone, or the
like, and the resin may be compounded with fillers, friction modifiers,
fibers, stabilizers and/or the like. When the inventive belt is used with
an UHMWPE friction partner, the friction coefficient may be 2.5 to 6
times lower than observed with conventional nylon fabrics and UHMWPE. The
inventive belt also has improved abrasion resistance over conventional
belts, and the anti-static properties remain even after long term use.
Such drive system embodiments may have general structure of the test
systems illustrated in FIGS. 3 and 4, namely, pulleys, belts, support
mechanisms for the belt in between the pulleys, and motor drives. Instead
of sliding weights on top of the belt there might be objects being
transported by the belt. Alternately the drive system may be for
transmitting power between pulleys, or for synchronizing pulley motion,
or the like, which might not require a support mechanism, but might also
include tensioners, idlers or other components.

[0038]Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing from
the spirit and scope of the invention as defined by the appended claims.
Moreover, the scope of the present application is not intended to be
limited to the particular embodiments of the process, machine,
manufacture, composition of matter, means, methods and steps described in
the specification. As one of ordinary skill in the art will readily
appreciate from the disclosure of the present invention, processes,
machines, manufacture, compositions of matter, means, methods, or steps,
presently existing or later to be developed that perform substantially
the same function or achieve substantially the same result as the
corresponding embodiments described herein may be utilized according to
the present invention. Accordingly, the appended claims are intended to
include within their scope such processes, machines, manufacture,
compositions of matter, means, methods, or steps. The invention disclosed
herein may suitably be practiced in the absence of any element that is
not specifically disclosed herein.

Patent applications by THE GATES CORPORATION

Patent applications in class Including discrete embedded fibers

Patent applications in all subclasses Including discrete embedded fibers